In a micro inductor used for a radio frequency integrated passive device (hereinafter, referred to as an “RFIPD”), an isolator, a transformer or the like, a thick dielectric or high-resistance layer having a thickness of 20 μm or more should be formed in a lower portion of the micro inductor so as to improve the quality factor (Q-factor) by decreasing insertion loss. However, since a dielectric layer has a restriction in dissipating heat generated from an inductor due to low thermal conductivity, it is difficult to manufacture a high-performance inductor. Thus, a material with excellent thermal conductivity should be formed in a lower portion of an inductor. When a material having low resistance is formed in the lower portion of the inductor, a large number of free electrons and holes that exist inside the corresponding material decrease the magnetic field strength of the inductor. Therefore, the insertion loss of the inductor is increased, and consequently, the Q-factor is decreased. However, when a high-resistance layer of 5 kΩ-cm or more is formed in the lower portion of the inductor, it is possible to use a material with relatively excellent thermal conductivity depending on the kind of material of the high-resistance layer, and a satisfactory Q-factor can be obtained because the insertion loss of the inductor is small.
A material having excellent thermal conductivity and high resistance includes III-V Group semiconductors (GaAs has a thermal conductivity of 0.46 W/cm-° C., and GaN has a thermal conductivity of 1.1 W/cm-° C.). However, there is a disadvantage in that these semiconductors are considerably expensive. On the other hand, silicon semiconductors have a considerably excellent thermal conductivity (1.31 W/cm-° C.), and the low manufacturing cost.
However, although a silicon wafer manufactured by the Czochralski method, which is generally used, has the low manufacturing cost, an oxygen component flows out from a quartz growth container when growing silicon crystals and the oxygen component serves as an n-type impurity, which makes it difficult to manufacture a high-resistance silicon wafer. Thus, it is general that an n-type or p-type silicon wafer is manufactured by adding phosphorous (P) or boron (B) to the silicon wafer manufactured by the Czochralski method. Meanwhile, in a case where a silicon wafer is manufactured by a float-zone method, a high-resistance silicon wafer can be easily manufactured because an oxygen component does not flow out from a growth container. However, there are disadvantages in that the silicon wafer manufactured by the float-zone method is higher in manufacturing cost than that manufactured by the Czochralski method, and it is difficult to manufacture a large-sized silicon wafer.
In addition, when an RFIPD, isolator or transformer is manufactured as described above, in order to improve the Q-factor, a thick dielectric layer having a thickness of 20 μm or more is formed, or a high-resistance wafer is used. Therefore, it is impossible to form an element such as a transistor manufactured on a low-resistance wafer simultaneously with the RFIPD, isolator or transformer. This is because when forming a dielectric layer having a thickness of 20 μm or more, it is difficult to perform a process of forming a dielectric layer and impossible to secure a uniform dielectric layer, and it is hardly possible to form electrode wires over a thick dielectric layer even though an element such as a transistor is formed on a low-resistance wafer.